Mandrels have been used to fabricate rocket motor housings. For example, U.S. Pat. No. 5,386,777, which is incorporated by reference, describes fabrication of rocket motor housings using soluble mandrels that are composed of polyvinyl alcohol (PVA) sheets. According to U.S. Pat. No. 5,386,777, a mandrel may be formed by wrapping a core or tube with a web or sheets of highly porous polyvinyl alcohol, then coating the formed mandrel with insulation and an epoxy impregnated fiber filament that is cured, typically by heat, to form the housing over the PVA mandrel or core.
There are certain disadvantages to the fabrication methodology taught in U.S. Pat. No. 5,386,777. That is, the polyvinyl alcohol web has limited thermal stability and decomposes at elevated temperatures. More specifically, polyvinyl alcohol undergoes significant thermal decomposition in air at temperatures between about 200-220 degrees C. See D. W. Van Krevelen, Properties of Polymers 3rd Edition, Elsevier Publishers, New York, 1997, page 642; Merck Index 12th Edition, Merck & Co., Whitehouse, N.J., page 1309. Polyvinyl alcohol also has a high viscosity. A material having a lower viscosity than polyvinyl alcohol at equal solute concentrations is desirable. Polyvinyl alcohol also has a significant creep upon heating. A material having less creep is desirable.
Polyvinyl alcohol also has a tendency to be chemically reactive since it has reactive functional groups pendant to its backbone (e.g., hydroxyl groups). A material that is more chemically inert than polyvinyl alcohol is desirable. These limitations make it difficult to fabricate rocket housings and nozzles from epoxy or thermosetting resin that requires high curing temperatures. Thus, a more suitable method for manufacture of a mandrel is desired.